Might also want an update routine to correct existing timestamps (because for example if comment.module is first enabled part-way through the life of a site when there is existing content then those existing nodes will have the last_comment_timestamp set to their changed timestamp but new nodes will have it set to their created timestamp. This can make the tracker listing appear pretty random, especially any of the original nodes that still have no comments are updated - their last_comment_timestamp will then be the timestamp of the latest revision before comment.module was enabled).

And probably also an update routine to ensure consistency of last_comment_timestamp (which could currently be a mixture of n.created and c.changed) for nodes with 0 comments. However my SQL is not good enough to make a core-worthy patch for that..!